This invention relates to a double cylinder lock assembly operable by a key from the interior or exterior, and in particular, to an assembly where a key is retained in the interior cylinder when the lock bolt is extended or placed in a locked position from the interior of the door, or when the key is already positioned within the interior cylinder keyway and the lock bolt is extended by operation of the exterior cylinder.
Deadbolt locksets in current use have been resorted to for the purpose of adding to security against break-ins by unauthorized persons. Such locksets comprise a deadbolt mechanism manipulated on the outside by a key actuated mechanism and on the inside, in the alternative, by either a thumb turn or a keyed cylinder inner trim. A single lock cylinder requires a key to actuate it from the exterior but utilizes a thumb turn at the interior. A double lock cylinder requires a key to actuate it from the interior as well as the exterior. There are environments in which the single lock cylinder is preferable, and other environments where the double lock cylinder is preferable. Usually this is determined by the needs of the owner of the premises and/or building code requirements.
The double lock cylinder or keyed cylinder inner trim, is devoid of a thumb turn and depends upon a key to be opened. The double cylinder lock effectively prevents an intruder from opening a door provided with such lock from the inside even after entry has been made by some other means. Hence, bulky or large articles are more difficult to remove from the premises. Where double cylinder locks are employed, it is desirable and sometimes required that the key not be extractable from the interior cylinder when the lock bolt is extended to locked position by an occupant who remains inside. This is to assure ready unlocking capacity for rapid exit under panic conditions, such as fire.
Heretofore, rather complex and relatively costly mechanisms have been utilized to prevent extraction of the key from the interior cylinder when the lock bolt is extended by an occupant remaining on the inside of a door. Such complex mechanisms increase the cost of manufacturing double cylinder locksets and, due to their complexity, do not always function in a totally reliable manner. Accordingly, it is an object of this invention to provide a double cylinder lock of generally conventional construction, with only a modest modification being needed to retain the key in the lock when the locking bolt is extended to locked position by an occupant remaining inside, and wherein such modification is both relatively inexpensive and reliable.